Synthesis, characterization, and luminescence thermometry investigation of LiSrGd(WO₄)₃:Pr³⁺ phosphors

In this study, LiSrGd(WO₄)₃ (LSGW) phosphors doped with different concentrations of Pr³⁺ were synthesized via the traditional solid-solid method to explore their suitability for luminescence thermometry applications. Structural and morphological analyses using X-ray powder diffraction and scanning electron microscopy offered comprehensive insights. The energy gap value of LSGW, calculated at E _g = 3.69 eV for x = 5 at% Pr³⁺, suggested minimal alteration in the bandgap energy upon incorporation of Pr³⁺ ions into the LSGW host. The empirical energy levels for the free ion Pr³⁺ were derived from absorption and emission data are gathered from LSGW:Pr³⁺. The theoretical energy diagram and corresponding eigenstates for Pr³⁺ were calculated using block diagonalization of the Hamiltonian's matrix in the basis set of coupled states 〈4f²〉〈4f²τSLJ〉, considering intermediate coupling. Thermometric parameters were calculated using the luminescence intensity ratio strategy based on Pr³⁺ emission spectra for thermal coupled levels. Our findings revealed that the LIR1 (I ₅₃₁/I ₅₅₇) exhibited maximum absolute and relative sensitivities of 31.5 10^-4 K^-1 and 0.65% K^-1, respectively, at 300 K, accompanied by remarkably low-temperature uncertainty (δT) values ranging from 0.031 to 0.037 K in the 300-440 K temperature range. These results show the importance of LiSrGd(WO₄)₃:Pr³⁺ phosphors for optical applications.